An electric power steering system includes an overheat protection current value arithmetic unit that computes an overheat protection current value to which a current flowing into a motor is limited, and an overheat protection control unit that limits the current, which flows into the motor, on the basis of the computed overheat protection current value, suppresses heat dissipation caused by the current flowing into the motor, and thus protects onboard equipment. Information relevant to the computed overheat protection current value is stored. Whether a newly computed overheat protection current value is abnormal is decided based on comparison of the newly computed overheat protection current value with the stored information relevant to the overheat protection current value.
